Machines that have relatively movable parts include bearings. In those situations where there is direct contact between relatively moving parts, consideration must be given to the problem of wear. Typically, bearing materials are selected and/or a lubricant is used so that adequate service life is obtained and so that the risk of catastrophic failure is minimized. In some machines, lubrication is provided by process fluid. One example of such a machine is a sealless pump (also referred to as a canned motor/pump or magnetic drive pump) which is used to pump fluids that must be isolated from the ambient environment. In one type of canned motor/pump, a motor stage and a pump stage are disposed within a single housing and include a common rotor coupled to a pump impeller. The rotor is supported by radial journal and axial thrust bearings lubricated with process fluid. These bearings are made of a relatively soft carbon or wear resistant ceramic material. Typically, lubrication by the process fluid is marginal, and intermittent dry operation is encountered. As a result, wear occurs at the bearings between the rotor and the stator.
Bearing wear monitors are often used in the foregoing environment to detect when bearing wear has occurred to an appreciable extent. Such bearing wear monitors include a plurality of sensor assemblies, each of which includes one or more sense windings disposed in the stator and a target disposed on the rotor. Such sensor assemblies, however, are positioned within the axial extent of the stator windings of the motor, and thus are exposed to electromagnetic interference, which adversely affects the operation of the sensors. In an attempt to remedy this situation, it has been proposed to provide electromagnetic shields in the stator and rotor of the motor. The stator shield is disposed between the motor stator windings and the sense windings whereas the rotor shield is disposed between the rotor structure and the target of the sensor assembly. While this shielding apparatus may be effective to provide adequate immunity against electromagnetic interference, such a shielding configuration requires a relatively long axial length between the sensor assembly and the ends of the motor stator windings. In addition, such a shielding configuration utilizes a relatively large amount of material in manufacturing and is likely to experience vibration resulting from shaft dynamic problems.